INTERSTELLAR OXIDE GRAINS FROM THE TIESCHITZ ORDINARY CHONDRITE

MOST material in the Solar System has an isotopic composition that rep resents an average of the different stars that contributed material to the protostellar cloud. Primitive meteorites, on the other hand, pres erve grains that retain the isotopic signatures of their individual st ellar sources(1) and thus provide valuable insight into stellar and ga lactic evolution, nucleosynthesis, and solar nebular processes. A larg e number of pre-solar silicon carbide, graphite and diamond grains hav e now been isolated(1,2), but only three interstellar oxide grains hav e hitherto been recovered(3-7), even though oxygen-rich stars are beli eved to be the dominant source of dust in the Galaxy(8,9). We report h ere the isolation of 21 interstellar oxide grains from the Tieschitz m eteorite. The grains exhibit a wide range of oxygen isotope compositio ns, indicating that they originated in several distinct stellar source s having different masses and initial compositions. There is also evid ence for the presence of the short-lived radionuclide Al-26 in nine of the grains at the time they formed. Although the isotopic composition s of many of the grains are consistent with both observations and theo retical models of oxygen-rich red giant stars, a significant fraction have no observed stellar counterpart.